Air Conditioning

Trouble Shooting Your A/C System


System is not cooling properly


Cold at idle, warmer when raising engine RPM’s

Make sure the Water Valve is positioned correctly

The water valve is a directional valve and should be installed with the arrow pointing towards the water pump, it should be connected to the heater hose that runs from the heater core to the water pump. If the water valve is connected to the incorrect hose it allows water to circulate through the system via the heater core overpowering the cooling effect of the A/C coil, (normally the air conditioning is functioning properly).

Step 1: Check the placement of the water valve, correct if needed. (In some cases changing the location of the water valve may not fix the above problem.) Continue to the next step.

Step 2: If changing the location of the water valve does not rectify the issue, then possibly the water valve is permanently damaged and may need to be replaced. To check the integrity of the water valve completely remove the water hoses for the heater core and “loop” together. (This will remove the heater system completely from the possibilities) If the system now cools, replace the water valve.

Verify Adequate Air Flow to Condenser

For an air conditioning system to function properly there has to be adequate airflow across the condenser. The function of the condenser is to dissipate heat, without proper airflow your system will not cool correctly in the cabin of your vehicle.

Step 1: Connect gauges to a/c hoses. The pressures should be: with the ambient temp is 90, low side pressures should be between 10-25 psi, high side pressures should be between 150-275 psi.

Step 2: If the low side pressures are normal and the high side pressures are high then there might be an airflow issue, continue to next step.

To test airflow to Condenser do the following three tests:

Step 1: Place a piece of paper on the condenser with the car in idle and see if the paper is held in place.

Step 2: With the car in idle, attach gages, and place a large capacity fan in front of the condenser. What happens to the pressures?

Step 3: With the car still in idle and gages attached, pour water down the front of the condenser. What happens to the pressures?

If the paper is held in place you are at least getting some airflow. If the high side decreases during tests 2 & 3 then your condenser is not getting enough air which is causing your system to not cool properly. To correct this issue you will need a more powerful mechanical fan.

Confirm correct Refrigerant charge in System:

All of our systems should be charged with 24oz or 1.5 lbs of R134 Refrigerant only. If overcharged you will need to evacuate the system and recharge with the correct amount.

What the measurements mean:

Low Temp and High Pressure seem to be equal… You have a malfunctioning expansion valve that is stuck open. High Side is extremely high and Low Side is extremely low (possibly into the vacuum)…

There is a blockage in the system. Remove hoses and blow compressed air through in both directions. If pressures don’t change its possible that your expansion valve is stuck closed and would have to be replaced.

Compressor Concerns:

This is often misdiagnosed as a problem for the system not cooling properly. If you have a noisy compressor it is due to improper charging of refrigerant. An overcharged (more than 24oz or 1.5 lbs R134) compressor can cause rattling.

If you have any more questions or concerns with your Classic Auto Air A/C System you can contact one of our Master Techs and they can help diagnose any issue you are having.


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